Antibodies to hnRNP core protein A1 in connective tissue diseases

We investigated the specificity of circulating autoantibodies to a heterogeneous nuclear ribonuclear protein A1 (hnRNP A1), obtained by recombinant DNA technique, in different rheumatic diseases: systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), scleroderma, primary Sjogren's syndrome (SS), idiopathic Raynaud (IR), mixed connective tissue disease (MCTD), and healthy donors. All sera were tested by ELISA on hnRNP A1 protein. Positive values were obtained in 22% SLE, 19% scleroderma, 10% IR, 40% (2/5) MCTD, 5% SS, and 50% RA patients. The majority of patients reacted with the aminoterminal part (UP1) of hnRNP A1; however, some RA patients reacted also with the carboxy-terminal part that shows partial homology with keratin. Therefore, hnRNP A1 (UP1) can be considered a target of antinuclear autoimmunity in various rheumatic disorders.